US 7400946 B2 Abstract A method and apparatus for measuring the velocity of a vehicle are provided. An acceleration measurement received from an accelerator and RGI data received from an external information server are stored and an irregularity constant of the accelerator is determined. It is determined whether the vehicle is in a stationary state by analyzing the acceleration measurement. If the vehicle is not in the stationary state, the inclination angle of a road on which the vehicle is traveling is calculated using a plurality of three-dimensional shape points included in the RGI data. A gravity acceleration component is compensated for from the acceleration measurement using the road inclination angle. The velocity of the vehicle is calculated using the compensated acceleration measurement.
Claims(13) 1. A method of measuring the velocity of a vehicle, comprising the steps of:
(1) storing an acceleration measurement received from an accelerator and route guidance information (RGI) data for route guidance of the vehicle, received from an external information server, to use to determine an irregularity constant of the accelerator;
(2) determining whether the vehicle is in a stationary state by analyzing the acceleration measurement and calculating the inclination angle of a road on which the vehicle is traveling using a plurality of three-dimensional shape points included in the RGI data if the vehicle is not in the stationary state;
(3) compensating for a gravity acceleration component from the acceleration measurement using the road inclination angle; and
(4) calculating the velocity of the vehicle using the compensated acceleration measurement.
2. The method of
_{c }at a predetermined time point is equal to a previous acceleration measurement f_{pre }and the number of successive occurrences of f_{c }is equal to or greater than a predetermined value.3. The method of
determining a current position of the vehicle on the RGI data;
determining whether the present position of the vehicle matches with any of a plurality of shape points included in the RGI data; and
calculating a road inclination angle between the shape point and a previous shape point, if the present position of the vehicle matches any of the shape points.
4. The method of
5. The method of
calculating a movement distance d(x, y) on an x-y plane and a movement distance dz along a z axis from a first shape point (x
_{1}, y_{1}, z_{1}) and a second shape point (x_{2}, y_{2}, z_{2}) by which the road inclination angle is calculated; andcalculating the road inclination angle θ by computing d(x, y) and dz according to
6. The method of
calculating a movement distance d(x, y) on an x-y plane and a movement distance dz along a z axis from a first shape point (x
_{1}, y_{1}, z_{1}) and a second shape point (x_{2}, y_{2}, z_{2}) by which the road inclination angle is calculated; andcalculating the road inclination angle θ by computing d(x, y) and dz according to
7. The method of
8. An apparatus for measuring the velocity of a vehicle, comprising:
an acceleration measurer for measuring a current acceleration of the vehicle through an accelerator mounted on the vehicle;
an acceleration storage for storing an acceleration measurement received from the acceleration measurer according to measured time;
a gravity acceleration compensator for calculating the inclination angle of a road on which the vehicle is traveling using a plurality of three-dimensional shape points included in RGI data received from an external server and compensating for a gravity acceleration component from the acceleration measurement using the road inclination angle; and
a velocity calculator for calculating the velocity of the vehicle using the compensated acceleration measurement.
9. The apparatus of
10. The apparatus of
11. The apparatus of
12. The apparatus of
_{1}, y_{1}, z_{1}) and a second shape point (x_{2}, y_{2}, z_{2}) by which the road inclination angle is calculated, and calculates the road inclination angle θ by computing d(x, y) and dz according to13. The apparatus of
Description This application claims priority under 35 U.S.C. § 119 to an application entitled “Method and Apparatus for Measuring Velocity of Land Vehicle Using Accelerometer and Route Guidance Information Data” filed in the Korean Intellectual Property Office on Dec. 1, 2003 and assigned Serial No. 2003-86438, the contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates generally to a method and apparatus for measuring the velocity of a land vehicle, and in particular, to a method and apparatus for measuring the velocity of a land vehicle using an accelerometer and RGI (Route Guidance Information) data. 2. Description of the Related Art In general, vehicles, such as aircraft, ship, land vehicle, etc., are equipped with navigation systems for positioning the vehicles and providing destination routing. To position a vehicle and provide a route to a destination, a navigation system must decide the position of the vehicle accurately. Therefore, the navigation system is usually provided with a measuring device for determining its own position. The measuring device can determine the position using an external aid, or using an internal sensor. An example of the case of the external aid is a GPS (Global Positioning System), and an example of the case of the internal sensor is a DR (Dead Reckoning) system using an inertial sensor. The DR system with an inertial sensor or an Inertial Navigation System (INS) is a navigation system first developed by the Massachusetts Institute of Technology (MIT) in the U.S. in the early 1950s and deployed for practical use in the 1960s. The INS calculates the velocity and position of a vehicle using a gyroscope for sensing rotation and an accelerometer for sensing linear movement. The basic operational principle of the INS may be summarized as follows. The INS first calculates the vehicle direction (angle) of a vehicle by integrating angular velocities output from the gyroscope, compensates the output of the accelerator for the gravity acceleration, and integrates the compensated accelerator outputs. Thus, the INS autonomously calculates the current velocity and position of the vehicle. While the INS advantageously provides accurate and continuous navigation data for a short term, errors are accumulated over time due to the integration. Therefore, a very expensive accurate gyroscope and accelerator are required to implement the INS. To ensure higher accuracy and long-term stability, the INS is usually used in conjunction with a non-inertial auxiliary sensor such as a magnetic compass and the GPS rather than independently. As described above, the velocity of a vehicle is calculated by combining velocity information from an accelerator with the vehicle direction information from a gyroscope. Accurate calculation of the velocity of the vehicle in a three-dimensional space requires three one-axis gyroscopes arranged perpendicular to one another and three one-axis accelerators, also arranged perpendicular to one another. Yet, the vehicle velocity can be obtained with the use of fewer sensors according to the type of the vehicle. For example, in the case of a land vehicle, since the rolling of a shaft connecting the front to the rear of the land vehicle and its linear movement in a perpendicular direction to a road surface are negligible, as many sensors as used to sense the rolling and linear movement can be saved. To calculate a velocity vector of a vehicle traveling on a road, the DR system with an inertial sensor must measure the direction of the vehicle and the velocity of the vehicle in a direction of motion. A gyroscope on an axis perpendicular to the plane of a vehicle shaft is required to measure the direction of the vehicle. Also, to measure the velocity of the vehicle along the direction of motion, the inclination angle of the road must be measured in addition to the use of an accelerator installed in the direction of the vehicle shaft. The reason for measuring the inclination angle of the road in calculating the velocity vector of the vehicle in the DR system is to calculate the gravity acceleration involved in the output of the accelerator from the road inclination angle. That is, because the gravity acceleration is applied in a direction perpendicular to the surface of the elliptical earth (the surface of a sphere perpendicular to the gravity acceleration), if the axis of direction of the accelerator, fixed in a predetermined direction on the vehicle, is changed due to a change in the road inclination angle, a gravity acceleration component in the output of the accelerator is also changed. Therefore, the pure motion acceleration of the vehicle is achieved only when the gravity acceleration, varying with the road inclination angle, is removed from the output of the accelerator. However, because the motion acceleration in the direction of motion and the gravity acceleration component cannot be distinguished from each other without knowledge of the road inclination angle, an error of the gravity acceleration component is involved in measuring the velocity of the mobile terminal. As the vehicle The measurement {right arrow over (a)} includes an actual acceleration component {right arrow over (ra)} and a gravity acceleration component {right arrow over (g)}. This gravity acceleration component, {right arrow over (g)}, which is measured together with a variation in an actual velocity, is an error factor for velocity measuring. Hence, the vehicle DR system must subtract the gravity acceleration {right arrow over (g)} from the acceleration measurement {right arrow over (a)} to measure an accurate velocity of the vehicle and the road inclination angle is required to measure the gravity acceleration {right arrow over (g)}. To this end, the DR system must be additionally equipped with a gyroscope or a clinometer. Traditionally, a gyroscope is responsible for measuring a road inclination angle. Therefore, the vehicle-DR system uses two or more gyroscopes: one for deciding the direction of a vehicle and another for calculating the road inclination angle. Since the gyroscopes are basically sensors for measuring variations, the vehicle DR system, which measures the road inclination angle using a gyroscope, integrates the outputs of the gyroscope to obtain the road inclination angle. Therefore, an error component of the gyroscope is integrated in the integration process, thereby accumulating errors over time in estimating the road inclination angle. To calculate the road inclination angle, thus, the gyroscope is used not alone, but in conjunction with an auxiliary sensor without errors being accumulated. Although a sensor such as a clinometer can be adopted to calculate the accurate road inclination angle, an existing accelerator is generally used as the auxiliary sensor to minimize the number of sensors used. Despite the advantage that no errors are accumulated in the road inclination angle information, however, this method is sensitive to the performance of the accelerator and insensitive to the change of the inclination angle. Moreover, the use of a low cut-off frequency to separate the gravity component leads to a time delay. As described above, the conventional vehicle DR system uses an additional gyroscope for estimating a road inclination angle because the road inclination angle cannot be calculated only using an accelerator. However, the addition of an expensive gyroscope to the DR system makes it impossible to realize a low-price DR velocity measuring device. An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method for implementing a low-price Dead Reckoning (DR) velocity measuring device using an accelerator and Route Guidance Information (RGI) data. Another object of the present invention is to provide an apparatus and method for calculating the inclination angle of a road on which a vehicle is traveling using shape points included in the RGI data, and measuring a gravity acceleration component included in an acceleration component of the vehicle using the road inclination angle. A further object of the present invention is to provide an apparatus and method for measuring a gravity acceleration component using an accelerator and the RGI data and measuring the velocity of a vehicle using the gravity acceleration component. The above objects are achieved by providing a method and apparatus for measuring the velocity of a vehicle are provided. According to one aspect of the present invention, in a method of measuring the velocity of a vehicle, an acceleration measurement received from an accelerator and RGI data received from an external information server are stored and an irregularity constant of the accelerator is determined. It is determined whether the vehicle is in a stationary state by analyzing the acceleration measurement. If the vehicle is not in the stationary state, the inclination angle of a road on which the vehicle is traveling is calculated using a plurality of three-dimensional shape points included in the RGI data. A gravity acceleration component is compensated for from the acceleration measurement using the road inclination angle. The velocity of the vehicle is calculated using the compensated acceleration measurement. According to another aspect of the present invention, in an apparatus for measuring the velocity of a vehicle, an acceleration measurer measures a current acceleration of the vehicle through an accelerator mounted on the vehicle, an acceleration storage stores an acceleration measurement received from the acceleration measurer according to measured time, a gravity acceleration compensator calculates the inclination angle of a road on which the vehicle is traveling using a plurality of three-dimensional shape points included in the RGI data received from an external server and compensates for a gravity acceleration component from the acceleration measurement using the road inclination angle, and a velocity calculator calculates the velocity of the vehicle using the compensated acceleration measurement. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. A navigation system is typically comprised of a server and a terminal. The server transmits RGI data to the terminal mounted on a vehicle, and the terminal provides a route guidance service to a user based on the RGI data. The RGI data includes the coordinates of the road on which the vehicle is traveling. The present invention pertains to an apparatus and method for accurately measuring the velocity of a vehicle by measuring the inclination angle of a road on which the vehicle is moving using the coordinates of the road included in the RGI data, compensating for a gravity acceleration component in an acceleration measurement of an accelerator using the road inclination angle. The navigation system will be described below. Lets denote one shape point (a second shape point) by P Thus, the road inclination angle θ is determined according to Equation (4)
Referring to The velocity measuring apparatus determines whether the vehicle is in the stationary state by comparing current measurement data f However, it may occur that f To avoid the wrong decision of determining the vehicle in the stationary state in the above cases, steps S If it turns out that the vehicle actually is in the stationary state in steps S If it is determined that the vehicle is in the stationary state, that is, the vehicle is moving in step S If P(t) matches with S(t), a road inclination angle is calculated using the (x, y, z) coordinates of the shape point S(t) and the previous shape point S(t-1) in step S To calculate the road inclination angle, the velocity measuring apparatus must receive RGI data from the server in the navigation system, though the RGI reception step is not shown. After step S To compensate for the gravity acceleration component, B is first subtracted from f, resulting in the difference {circumflex over (f)}. Thus, from Equation (6), {circumflex over (f)} is expressed according to Equation (7) as
The road inclination angle θ was calculated in step S In step S
The velocity V of the vehicle is computed by integrating the acceleration a in step S
The gravity acceleration compensator The velocity calculator In accordance with the present invention as described above, the inclination angle of a road on which a vehicle is moving is calculated using two shape points in a three-dimensional space included in RGI data and a gravity acceleration component is compensated for from measurement data from an accelerator using the road inclination angle in a navigation system. Therefore, a vehicle velocity measuring apparatus can be realized with a reduced number of gyroscopes and thus reduced cost. While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Patent Citations
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